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Project Specific Discussions => Filters/Equalizers => Topic started by: declankennedy on June 07, 2019, 03:57:44 PM

Title: High Pass Filter for Compressor Sidechain Input
Post by: declankennedy on June 07, 2019, 03:57:44 PM
Hi everyone -

I'm attempting to build a high pass filter to be used as a sidechain input for my Dramastic Obsidian stereo compressor. The built-in HPF is a little to high (150 Hz) for our liking. One issue is that the sidechain input is mono. Our first crude attempt involved Y-cable multing off of the right and left inputs, summing those mults with 1K resistors, and then placing capacitors in series to create the filter. I attached a diagram that will give you a visual of this.

The goal is to have a copy of the input (preferably a summed signal of left & right) to send through a high pass filter (90Hz cutoff) and into the sidechain input (10K Ohm impedance). What's the best way to go about this?

Thanks.

Declan
Title: Re: High Pass Filter for Compressor Sidechain Input
Post by: abbey road d enfer on June 07, 2019, 05:25:58 PM
Hi everyone -

I'm attempting to build a high pass filter to be used as a sidechain input for my Dramastic Obsidian stereo compressor. The built-in HPF is a little to high (150 Hz) for our liking.
Wouldn't it be easier to modify the built-in HPF?

Quote
One issue is that the sidechain input is mono. Our first crude attempt involved Y-cable multing off of the right and left inputs, summing those mults with 1K resistors, and then placing capacitors in series to create the filter. I attached a diagram that will give you a visual of this.
This should work; you would have the possibility to experiment with different values, even make them switchable.
Title: Re: High Pass Filter for Compressor Sidechain Input
Post by: john12ax7 on June 07, 2019, 07:50:36 PM
The passive approach would have crosstalk issues,  as you would be injecting some left signal into right and vice versa.
Title: Re: High Pass Filter for Compressor Sidechain Input
Post by: declankennedy on June 12, 2019, 11:18:13 AM
The passive approach would have crosstalk issues,  as you would be injecting some left signal into right and vice versa.

Yes, we did find crosstalk when we doing testing. Is an active approach the only way to go about this project? Can the directional capacitors perhaps be used differently in the passive approach so as to eliminate the crosstalk? Obviously passive is far simpler, so let me know if you think it can be done in any way.
Title: Re: High Pass Filter for Compressor Sidechain Input
Post by: abbey road d enfer on June 12, 2019, 12:02:36 PM
Yes, we did find crosstalk when we doing testing. Is an active approach the only way to go about this project? Can the directional capacitors perhaps be used differently in the passive approach so as to eliminate the crosstalk? Obviously passive is far simpler, so let me know if you think it can be done in any way.
You may find a better compromise using higher value resistors, but it won't be perfect. Indeed, only an active solution can approach perfection.